Age as the second parameter in NGC 288/NGC 362? I. Turnoff ages: A purely differential comparison

We present deep V, I photometry of the globular clusters NGC 288, 362, and 1851 obtained during a single observational run under strictly homogeneous conditions. We use the bimodal horizontal branch (HB) of NGC 1851 as a "bri dge" to obtain the optimum relative match between the HBs of NGC 288 and NG C 362. In this way we can effectively remove the uncertainties associated w ith distance, reddening, and inhomogeneities in the absolute calibration, t hus obtaining a very robust, purely differential estimate of the age differ ence between these two clusters. According to the bridge test, NGC 288 is f ound to be older than NGC 362 by 2 +/- 1 Gyr. This result is fully confirme d also by all classical differential age diagnostics, either based on the l uminosity (DeltaV(TO)(HB)) or color [delta (V-I)(@2.5)] of the main-sequenc e turnoff point.